3 use std::f64::consts as f64;
4 use syntax::ast::{Lit, LitKind, FloatTy};
8 /// **What it does:** Checks for floating point literals that approximate
9 /// constants which are defined in
10 /// [`std::f32::consts`](https://doc.rust-lang.org/stable/std/f32/consts/#constants)
12 /// [`std::f64::consts`](https://doc.rust-lang.org/stable/std/f64/consts/#constants),
13 /// respectively, suggesting to use the predefined constant.
15 /// **Why is this bad?** Usually, the definition in the standard library is more
16 /// precise than what people come up with. If you find that your definition is
17 /// actually more precise, please [file a Rust
18 /// issue](https://github.com/rust-lang/rust/issues).
20 /// **Known problems:** If you happen to have a value that is within 1/8192 of a
21 /// known constant, but is not *and should not* be the same, this lint will
22 /// report your value anyway. We have not yet noticed any false positives in
23 /// code we tested clippy with (this includes servo), but YMMV.
32 "the approximate of a known float constant (in `std::fXX::consts`)"
35 // Tuples are of the form (constant, name, min_digits)
36 const KNOWN_CONSTS: &'static [(f64, &'static str, usize)] = &[(f64::E, "E", 4),
37 (f64::FRAC_1_PI, "FRAC_1_PI", 4),
38 (f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5),
39 (f64::FRAC_2_PI, "FRAC_2_PI", 5),
40 (f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5),
41 (f64::FRAC_PI_2, "FRAC_PI_2", 5),
42 (f64::FRAC_PI_3, "FRAC_PI_3", 5),
43 (f64::FRAC_PI_4, "FRAC_PI_4", 5),
44 (f64::FRAC_PI_6, "FRAC_PI_6", 5),
45 (f64::FRAC_PI_8, "FRAC_PI_8", 5),
46 (f64::LN_10, "LN_10", 5),
47 (f64::LN_2, "LN_2", 5),
48 (f64::LOG10_E, "LOG10_E", 5),
49 (f64::LOG2_E, "LOG2_E", 5),
51 (f64::SQRT_2, "SQRT_2", 5)];
56 impl LintPass for Pass {
57 fn get_lints(&self) -> LintArray {
58 lint_array!(APPROX_CONSTANT)
62 impl LateLintPass for Pass {
63 fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
64 if let ExprLit(ref lit) = e.node {
65 check_lit(cx, lit, e);
70 fn check_lit(cx: &LateContext, lit: &Lit, e: &Expr) {
72 LitKind::Float(ref s, FloatTy::F32) => check_known_consts(cx, e, s, "f32"),
73 LitKind::Float(ref s, FloatTy::F64) => check_known_consts(cx, e, s, "f64"),
74 LitKind::FloatUnsuffixed(ref s) => check_known_consts(cx, e, s, "f{32, 64}"),
79 fn check_known_consts(cx: &LateContext, e: &Expr, s: &symbol::Symbol, module: &str) {
81 if s.parse::<f64>().is_ok() {
82 for &(constant, name, min_digits) in KNOWN_CONSTS {
83 if is_approx_const(constant, s, min_digits) {
87 &format!("approximate value of `{}::consts::{}` found. \
88 Consider using it directly", module, &name));
95 /// Returns false if the number of significant figures in `value` are
96 /// less than `min_digits`; otherwise, returns true if `value` is equal
97 /// to `constant`, rounded to the number of digits present in `value`.
98 fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool {
99 if value.len() <= min_digits {
102 let round_const = format!("{:.*}", value.len() - 2, constant);
104 let mut trunc_const = constant.to_string();
105 if trunc_const.len() > value.len() {
106 trunc_const.truncate(value.len());
109 (value == round_const) || (value == trunc_const)